Porcelain enamel for direct application to metal and process for producing the same



Patented July 22, i952 PORCELAIN ENAMEL FOR DIRECT APPLICA- TION' TO METAL AND PROCESS FOR PRO- 'DUCING THE SAME Eugene E. Bryant, Bedford, Ohio, assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Army No Drawing. Application February 15, 1949,

:Serial No. 76,652

- 19 Claims.

' This invention relates as indicated to porcelain enamels for direct application to metal, and to a process for producing the same. It is primarily concerned withthe provision of such an enamel characterized by improved density. and strength, and, in its preferred embodiment, bythe fact that it is alsoacid-resistant. V

This application is a continuation-inpart of my"application'Seri alNo. 529,816,. filed April 6,

4==tn w ab do ed. Most porcelain enamels which are applied directly to themetalyand are accordingly generically defined as ground coatsjeven ,though no finished coat may be applied thereover, generally during the firing operation, have formed therein a substantial amount of bubbles of appreciable size. This bubble structure of ground coats isgenerally attributed to various causes such as the occurrence on the metal surface of a certain amount of oxide of the metal which may be present before the application of the enamel slip, or which is formed by an oxidation of the base metal prior to and during the firing stage. The presence of oxygen in the atmosphere in which the enamel is fired, and'also the possibility of oxygen liberation from slip components such as the normal clay content thereof, have also been charged with being the reason for bubble generation during the firing step.

The prior art has endeavored to overcome this difiiculty bythe use of a controlled atmosphere in the furnace in which the firing operation is performed- The use of "a controlled or reducing atmosphere in the furnace is, however; anexpensive expedient, and it is the principal object of my invention to avoid the'necessity of using such atmospherer- A further object of my invention is to provide adense' strongvitreous. acid-resisting enamel coating, applicable to a ferrous base by direct firing thereon.

yOther'obJ'ects of my invention will appear as .the description proceeds. v

related ends, said invention then comprises the features hereinafter fully described and particularly pointed out in the claims, the following description setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principle of the invention may be employed.

Broadly stated, this invention comprises providing a porcelain enamel which is adapted for direct application to steel for the'production of a dense and strong coating by the inclusion therein of a reducing agent.

Because the factors which are responsible for the generation of the objectionable structure apparently function in a relatively narrow range of conditions during the firing operations, the reducing agent which is selected for the purpose of counteracting the same must be effective in such narrow range. The reducing agent which I have found to be effective for the stated purpose is silicon metal which may be added to the enamel in the mill in the form of silicon metal, or in the form of ferrosilicon, the latter being an alloy of iron and silicon, and being the most economical form in which silicon metal is available for purposes such as this.

This particular reducing agent has been found to be efiective for the stated purpose in only certain types of enamel. The enamels in which silicon metal has been found effective as a reducing agent during the firing operation are those generally identified in the trade as acid-resisting enamels. They have the common characteristic of containing silica of at least about 4 0% and up. toabout as compared with a lower silica content of non-acid-resisting enamels. The enamels in which the use of silicon metal has been found effective have also had the common characteristic of containing a substantial amount, on the order of from about 2% to about 12% of titanium dioxide. It is not known whether there is some reaction. between the silicon metal and the titanium:content of the frit in the function of the formeras a; reducing agent during the firing step.

A raw batch mixture providing the desired silica and titanium dioxide for my enamel in accordance with the present invention, together with other suitable fritting agents, occupies the following ranges:

Table 1 Parts by Weight (Percent) From To About-- About-- Silica 40 65 Titanium Dioxide 2 12 15 25 l5 0 2O 0 8 Cobalt Oxide 0.5 3 Potash Carbonate 0 20 Potash Nitrate 0 10 Lithium Carbonate 0 5 Sodium Fluosilicate i 0 1'2 Manganese Oxide l) Y Z 0 4 It will be understood that the fritting agents in. the above table, other than the silica and titanium dioxide are interchangeable in a manner well known to the expert in the enamel art, that is, where the lower limit of a fritting agent is indicated as 0, it may be substituted by suitably raising the amount of an equivalent fritting agent.

'Those familiar with formulation will recognize that variations in the above ranges of such fritting agents may be used to supply essentially equal calculated yields and substitution of materials not listed may also be used to produce Parts by Weight (Percent) From To About- About- As illustrative of acid-resisting enamels of the character described, which are capable of use in carrying out my invention, the following specific examples are given:

A raw batch mixture is compounded according to Example A or B of Table 3:

The titanium dioxide content of raw batch mixtures whose silica content is of the order of 45 to 50 percentage parts by weight, as exemplified by Examples A and B, is preferably between about 3 and about 6 parts by weight.

These enamels, after being smelted at a temperature on the order of about 2300 F. will be fritted in the conventional manner, and then used as a mill charge, of which the following is representative.

It will be observed that each of the examples given above is characterized by the presence of a large percentage of silica and an appreciable amount of titanium dioxidein the raw batch mixture, and consequently in the frit. In order to prepare from the above described frits an enamel slip which, when fired directly on steel, will have the characteristics which form the principal objects of my invention, I add thereto uncombined silicon (silicon metal or ferrosilicon) in the equivalent proportions of ab0ut..5 to about 2 parts by weight per parts by weightof frit, together with other mill charge forming'agents, including principally clay and water. The followin table gives illustrative ranges of ingredients for such a mill charge;

Table 4 Parts by Weight (Percent) To About- From About.

cpcooooecn 1 Including 0 to about 1 part of bentonite. 7

For instance, a mill charge may be formed by compounding the ingredients as follows:

Table 5 Parts by weight Fri1: 100. 7 Silicon metal. from about-.5 to about 2.

by weight of a member of the group applications or operating conditions. For example, additions of quartz or feldspar may be made to increase resistance to firing. Bentonite may be added or changes in clay may be made to adjust the suspension. So called set-up electrolytes such as magnesium carbonate, sodium nitrite, potash carbonate may be added or substiituted for hydrated borax.

Ferrosilicon (electric furnace grade) with more than 50 silicon may be used to replace the silicon metal in the mill addition. I prefer the about 1480" F. to about 1700 F., depending on variations in formulation, for a period of about 4 minutes when 20-gauge sheet iron is used as the base metal. For the mill charge set forth in Table 5, I prefer a firing temperature from about 1560 F. to 1600 F.

The foregoing illustrative examples of my invention will enable those skilled in the art to make the customary modifications in adapting the same to particular uses.

A fired enamel coating prepared in the manner described will, under the microscope, show a marked reduction, in many cases a total absence of, the bubble structure which characterizes most ground coats, and which is responsible for the low strength and other undesirable properties of conventional ground coats.

As indicated, my invention is applicable not only to the use of ground coats, over which a finished coat will ultimately be applied, but also, because of the improved characteristics of the ground coat, the same may be used as a finished coat, 1. e. without the application thereover of an additional finished coat.

When the enamel coating of my invention is to be used as a ground coat, the normal dry weight of application will be on the order of about 20 grams per square foot of area covered. If the same enamel is to be used as the finished coat, then a second coat may be applied over the first, the second being applied at a normal dry weight on the order of about 40 grams per square foot of area covered, making a total of about 60. The foregoing values are intended merely as illustrative, and thoseskilled in the art may, for particular purposes, vary the weights of application which have been given as examples.

I claim:

1. An enamel slip providing a dense strong vitreous acid-resisting coat when directly fired on metal, such characteristics being imparted thereto by the presence of from about 40 to about 65 parts by weight of silica, from about 2 to about 12 parts by weight of titanium dioxide, from about to about 18 parts by weight of boron oxide and from about to about parts by weight of at least one substance being a member of the group consisting of Nazo, K20, and U20, calculated per 100 parts by weight of frit; and

'water and from about 1 to about 10 parts by weight of clay and'from about .5 to about 2 parts consisting of siliconand ferrosilicon. a r r 2. An enamel slip providing a dense strong -vitreous acid-resisting 'coat when directly fired on metal, such characteristics being imparted thereto by the presence of from about 45 to about 50 parts by Weight of silica, from about 3 to about 6 parts by weight of titanium dioxide, from about 10 to about 18 parts by weight of boron oxide and from about 15 to about 25 parts by weight of at least one substance being a member of the group consisting of NazO, K20, and LizO, calculated per parts'by weight of frit, and by the addition to saidfrit in the mill charge of water and from about 1 to about, 10 parts by weight of clay and from about .5 to about 2 parts by weight of a member of the group consisting of silicon and ferrosilicon. Y

3. An enamel slip providing a dense strong vitreous enamel coating when directly fired on metal, whose frit has a calculated oxide content of about p v Parts by weight S102 40 to 65 T102 2 to 12 B203 10 to 18 At least one member of the group consisting of NazO, K20, L 15 to 25 00304 0.5 to 3 MnOz 1 to 3 said enamel slip further being characterized by the inclusion therein, as a mill addition to each 100 parts by weight of said frit of about Parts by weight A member of the group consisting of silicon and ferrosilicon .5 to 2 Clay 1 to '10 4. An enamel slip providing a dense strong vitreous acid-resisting coating 'when directly fired on metal and whose frit is produced by smelting a raw batch mixture comprising about 7 Parts by weight Silica 45 to 50 Titanium dioxide -1 3 to 6 Dehydrated borax 19 to 23 Feldspar 5 to 6.5 Soda ash 8 to 1'? Sodium nitrate 4 to 6 Cobalt oxide 2 Sodium fluosilicate 2.5 to 9 Manganese oxide 2 to 2.5

said enamel slip further being characterized by the inclusion therein. as a mill addition to each v100 parts by weight of said frit of about 7 p Parts by weight A member of the group consisting of silicon and ferrosilicon .5 to 2 Clay 1 to 10 5. An enamel slip providing a dense strong vitreous acid-resisting coating when directly fired on metal and whose frit is produced by smelting a'raw batch mixture comprising about said enamel slip further being characterized by the-inclusion therein, as a mill addition to the 7 frit of about? par-ts by weight ofclay, about .75 parts by weight of borax, and about .5 to about 2 parts by weight of a member of the group consisting of silicon and ferrosilicon, per 100 parts by Weight of said frit.

6. An enamel slip providing a dense strong vitreous acid-resisting coating when directly fired on meta'l'and whose frit is produced by smelting a raw "batch mixture comprising about Parts by weight Silica 49.5 Titanium dioxide 6.0 Dehydrated borax 19.0 Feldspar 5.0 Soda ash 8.0 Sodium nitrate -6.0 Cobalt oxide 2.0 Sodium fiuosilicate 9.0 Manganese oxide 2.0 Bone ash 3.0

said enamel slip further being characterized by the inclusion therein, as a mill addition to each 100 parts by weight of said .frit of about Parts by weight A member of the group consisting of silicon and .ferrosilicon ..5 to 2 Clay 1 to 7. An enamel slip providing a dense strong vitreous :acid resisting coating when directly fired on metal and whose frit is produced by smelting a raw batch mixture comprising about Parts by Weight Silica 49.5 Titanium dioxide .6.0 Dehydrated. borax 19.0 Feldspar 5.0 Soda ash 8.0 Sodium nitrate 6.0 Cobalt oxide 2.0 Sodium fiuosilicate 9.0 Manganese oxide "g- 2.0 Bone ash 3.0

said enamel slip further being characterized by the inclusion therein, as a mill addition to the frit of about 7 parts by weight oi clay, about .75 parts by weight of borax, and about .5 to about 2 parts by weight of a member of the group consisting of silicon and ferrosilicon, per -100 parts by Weightof said frit. 7

8. An enamel slip providing a dense strong vitreous acid-resisting coating when directly fired on metal and whose frit is produced by smelting a raw batch mixture comprising about Parts by weight Silica 49.0 Titanium dioxide 4.5 Dehydrated borax 23.0 Feldspar 6.5 Soda ash 17.0 Sodium nitrate 4.0 Gobalt oxide i 2.0 Sodium fluosil-icate 2.5 Manganese oxide 12.5

said enamel slip further being characterized by the inclusion therein, as a mill addition to each 100 parts by weight. oi said frit of about Parts by weight A m ember of the group consisting of Silica 9. An enamel slip providing a dense strong vitreous acid-resisting coating when directly fired on metal and whose frit is produced by smelting a raw batch mixture comprising about Parts by weight Silica 49.0 Titanium dioxide .l 4.5

Dehydrated borax a, 3.0 Feldspar 6.5 Soda ash 17.0 Sodium nitrate 4.0 Cobalt oxide 2.0 Sodium fluosilicate 2.5 Manganese oxide ..F 2.5

said enamel slip further being characterized by the inclusion therein, as a 'mill addition to the frit of about 7 parts by Weight of clay, about .75 parts by weight of borax, and about .5 to about 2 parts by weight of a member of the group consisting of silicon and ferrosilicon, per 100 parts by Weight of said hit. 7

10. A process for producing a slip adapted to provide an acid-resisting vitreous enamel capable of being directly fired on metal, comprising adding to each 100 parts of frit havinga calculated oxide content of aboutv 7 Parts by weight S102 40 to 65 T102 2 to 12 B203 10 to 18 At least one member of the group consisting of NazO, K20, Li2O 15 130 25 C0304 0.5 to 3 M1102 l to 3 mill charge forming agents comprising water and about Parts byweight A member of the group consisting .of silicon and ferrcsilicon .5 to 2 Clay 1 to 10 and grinding said frit and additives together until not more than 8 grams per .50 cc. are retained on a 200 mesh sieve.

' 115A process for producing a slip adapted to provide an acid-resisting vitreous enamel capable of being directly fired on' metal, comprising smelting a mixture comprising about Parts by weight l,.. to Titanium dioxide 3 to 6 Dehydrated borax 19 to 23 Feldspar 5 to 6.5 Soda ash 8 to 17 Sodium nitrate 4m 6 Cobalt oxide 2 Sodium iiu'osilicate 2.5 to 9 Manganese oxide '2 to 2.5

at :a'temperature on the (order of 230.0" fritting the smeited :mixture; adding to' the frit':

wateryabout'll parts by weight of clay, about .75 partz-by"weight .-of 'borax, and. about .5ito 2 parts by weight ofa member oft-he groupjconsisting of silicon andierrosilicon, perparts by weight of said rfrit and grindingsaid f r-it and additives togetheruntil not more than 8 grams per 50 .cc.

are retained on a 200 mesh sieve.

12. A process iior producing an acid-resisting vitreous enamel coating directly fired on metal 9f." comprising fritting aziraw batch. mixture comprising aboutfl. i

' V Parts by weight Silica 45 to 50 Titanium dioxide 3 to 6 Dehydrated borax 19 to 23 F'eldspar to 6.5 Soda ash 8 to 1'7 Sodium nitrate 4 to 6 Cobalt oxide 2 Sodium fluosilicate 2.5 to 9 Manganese oxide 2 to 2.5

adding to each' 100 parts by weight of said irit: water'and about r v Parts by weight A member of the group consisting of silicon and ferrosilicon .5 to 2 Clay 1 to 10 grinding said frit and additives. together to form a finely divided intimate mixture, applying the ground mixture to a ferrous base and firing the same in a nonreducing atmosphere at a temperature on the order of about 1480 F. to about '1700 F.

13. A process for producing an acid-resisting vitreous enamel coating directly fired on metal comprising fritting a raw batch mixture comprising about a Parts by weight Silica 49.5 Titanium dioxide 6.0 Dehydrated borax 19.0 Feldspar -2 5.0 Soda ash 8.0 Sodium nitrate 6.0 Cobalt oxide 2.0 Sodium fiuosilicate 9.0 Manganese oxide 2.0 Bone ash 3.0

adding to each 100 parts of said frit: water, about 7 parts by weight of clay, about .75 part by weight of borax, and .5 to 2 parts by weight of a member of the group consisting of silicon and ferrosilicon; grinding said frit and additives together, applying the ground mixture directly to a metal base and firing the same in a non-reducing atmosphere at a temperature of about 1560 F. to about 1600 F. r

14. A process for producing an acid-resisting vitreous enamel coating directly fired on metal comprising fritting a raw batch mixture comp rising about Parts by weight I parts by weight of clay and from about .5 to

Silica 49.0 Titanium dioxide 4.5 Dehydrated borax 23.0

Feldspar 6.5

Soda ash 17.0 Sodium nitrate 4.0 Cobalt oxide 2.0 Sodium fluosilicate 2.5 Manganese oxide 2.5

- Silica about 2 parts by weight of a member of the group consisting of silicon and I ferrosilicon; grinding said frit and additives together to form a finely divided intimate mixture; applying the ground mixture directly to a metal base and firing the same inia non-reducing atmosphere. I '16. An enamel slip providing a dense vitreous enamel coating when directly fired on metal and whose frit is provided by. smeltingfa raw batch mixture comprising about Parts by weight Titanium dioxide Dehydrated borax I Cobalt oxide At least one member of the group consisting of soda'ash, sodium nitrate, I potash carbonate, potash nitrate, .lith- H ium carbonate, and-sodium fluosilicate (calculated as oxides) Manganese oxide 15a; 25 1 to 3 said enamel slip further being characterized by the inclusion therein, as a mill addition to each parts by weight of said frit of about Parts by weight A member of the group consisting of silicon and ferrosilicon .5 to 2 Clay 1 to 10 17. A process for producing an enamel slip adapted to provide an acid-resisting vitreous enamel capable of being directly fired on metal, comprising smelting a mixture which comprises about Parts by weight Silica 40 to ,65 Titanium dioxide 2 to 12 Dehydrated borax 15 to 25 Cobalt oxide 0.5 to 3 At least one member of the group consisting of soda ash, sodium nitrate, potash carbonate, potash nitrate, lithium carbonate and sodium fluosilicate (calculated as oxides) 15 to 25 Manganese oxide 1 to 3 at a temperature between about 2000 Fl and about 2500 F., fritting the smelted mixture, adding to each 100 parts by weight of said frit: water and about Parts by weight A member of the group consisting of silicon and ferrosilicon .5 to 2 Clay 1 to 10 and grinding said frit and additives together to form a finely divided intimate mixture.

18. A process for producing an acid-resisting vitreous enamel coat directly fired on metal, com- 1 l prising fritting a raw batch mixture comprising about Parts by weight Silica -140 to 65 Titanium dioxide 2 to 12 Dehydrated borax to Cobalt oxide 0.5 to3 At least one member of the group consisting of soda ash, sodium nitrate, potash carbonate, potash nitrate, lithium carbonate and sodium fiuosilicate (calculated asloxides). 15 to 25 Manganese oxide l 11:03

adding to each 100- parts of said frit: water and about Silica to Titanium dioxide 2to 12 Dehydrated borax 15 to 25 At least one member or the group con- 7,

sisting of soda ash, sodium nitrate,

potash carbonate, potash nitrate, lithium carbonate and sodium fluosilicate (calculated as oxides) 1 15 to 25 Manganese oxide 1 1to3 adding to eachv parts of said frit: water and about Parts by Weight A member of the group consisting'of silicon and ferrosilicon V .5 to 2 Clay l to 10 grinding said frit and additives together, applying the ground mixtures to a ferrous base and firing the same at a temperature on the order of about 1480 F. to about 1700 F.

EUGENE E. BRYANT.

REFERENCES CITED The following references aresof record in the file of this patent;

FOREIGN PATENTS Number Date a 5 OTHER REFERENCES Ceramic Abstracts, v. 12, page 293 (1933). Ceramic Industry, October 1940, page 64. 

1. AN ENAMEL SLIP PROVIDING A DENSE STRONG VITREOUS ACID-RESISTING COAT WHEN DIRECTLY FIRED ON METAL, SUCH CHARACTERISTICS BEING IMPARTED THERETO BY THE PRESENCE OF FROM ABOUT 40 TO ABOUT 65 PARTS BY WEIGHT OF SILICA, FROM ABOUT 2 TO ABOUT 12 PARTS BY WEIGHT OF TITANIUM DIOXIDE, FROM ABOUT 10 TO ABOUT 18 PARTS BY WEIGHT OF BORON OXIDE AND FROM ABOUT 15 TO ABOUT 25 PARTS BY WEIGHT OF AT LEAST ONE SUBSTANCE BEING A MEMBER OF THE GROUP CONSISTING OF NA2O, K2O, AND LI2O, CALCULATED PER 100 PARTS BY WEIGHT OF FRIT; AND BY THE ADDITION TO SAID FRIT IN THE MILL CHARGE OF WATER AND FROM ABOUT 1 TO ABOUT 10 PARTS BY WEIGHT OF CLAY AND FROM ABOUT .5 TO ABOUT 2 PARTS BY WEIGHT OF A MEMBER OF THE GROUP CONSISTING OF SILICON AND FERROSILICON. 